1. Field of the Invention
The present invention relates to the field of pilot-operated relief valves. More specifically, the present invention relates to a pilot-operated relief valve assembled in a single housing and having a non-flowing pilot-operated mechanism and a reverse flow prevention valve included as an integral part of the relief valve.
2. Prior Art Setting of the Invention
A well-known prior art design joins a pilot-operated control mechanism with a separate relief valve. The pilot-operated control mechanism is structurally secured to the relief valve with bolts or brackets or other similar attachment structure. The pilot mechanism is functionally connected to the inlet, outlet, and dome pressure areas of the relief valve with appropriate conduits. Such a design is illustrated, for example, in U.S. Pat. No. 3,568,706 to Weise.
Combining a pilot-operated control mechanism and a relief valve through a manifold structure is also taught in the prior art. See, for example, U.S. Pat. No. 5,769,113 to Alberts and McNeely.
The fabrication of pilot-operated relief valves as separate valve and pilot-operating assemblies affords some manufacturing advantages. The manufacture of separate components can increase flexibility in final design configurations and may also contribute to efficiencies in production. The use of separate assemblies for the relief valve and the pilot-operated control mechanism is, however, not without shortcomings. When the pilot-operating system and the relief valve are separate components, provision must be made for mechanically securing the pilot assembly to the relief valve.
Combining two separate structures can produce a relatively large composite assembly when the external dimensions of the combined structure are as large as the combined dimensions of the valve and pilot assembly. Communication must be established with the valve's inlet, outlet, and dome pressure areas, requiring the need for multiple conduits and their associated connections. Material and labor costs associated with the connection of the separate relief valve and pilot-operating mechanism contribute to the total cost of the final assembly. Each of the components required in joining the valve and pilot mechanisms is subject to damage during installation or usage.
Manifolded systems avoid some of the problems associated with separately constructed pilot valve assemblies. The manifolded systems eliminate the need for attachment hardware, pressure-communicating conduits and end connections. Manifolding also permits some reduction in the external dimensions of the composite pilot-operated relief valve assembly. These systems, however, require additional production processes and assembly procedures not required in the modular designs. For example, special manifolded test units are required to pre-test the pilots before they are installed. Another shortcoming is that the pilot-to-body sealing surfaces in the manifolded design are subject to corrosion damage that can render both the manifold and the valve body unusable.
The prior art also discloses unitary valve designs in which the primary pressure-responsive pilot components are installed in the valve cap so that the pilot-operating mechanism is an integral part of the valve structure. An example of such a valve may be seen in U.S. Pat. No. 2,890,714 to Greenwood and Francis. The valve is compact and provides a pilot-operated relief valve function without the need for a separate modular or manifolded configuration. The pilot-operating mechanism of the Greenwood et al. valve senses inlet pressure through an access passage extending through the main closure element. As the main valve opens to relieve high pressure, fluid flows through the access passage. Valves of this type are referred to as "flowing pilots".
Pilot-operated relief valves employing flowing pilots are associated with various shortcomings that limit their general usefulness. Undesired fluid loss can occur as the valve is relieving pressure. The flow of fluid through the access passage may also erode or otherwise damage the pilot-operating mechanism. Particulate matter in the flowing fluid can also obstruct the flow passages and other internal components within the pilot-operating mechanism.